1. Field of the Invention
This invention relates generally to a swing-type actuator for use in rotating disk data storage apparatus and particularly to a molded plastic actuator fabricated without fasteners.
2. Description of the Related Art
Magnetic disk data storage devices known in the art require a swing-type or rotation-type actuator to position the magnetic data sensing elements on the data recording tracks of a rotating magnetic disk. The magnetic data storage art is replete with swing-type actuators such as the actuator assembly 10 shown in FIG. 1. The overriding requirement known in the art is for mass-producible component constructions that are reliably high-performance. A typical actuator assembly known in the art, such as actuator assembly 10 in FIG. 1, includes an aluminum E-block 12 fabricated by machining an aluminum casting or extrusion. E-block 12 includes one or more actuator arms exemplified by actuator arm 14. A magnetic data head (not shown) is fixed to the end of each such actuator arm in a position exemplified by the position 16 on actuator arm 14. E-block 12 also includes a bore hole 18 disposed to receive a pivot assembly (not shown) for supporting the rotation of E-block 12 about a pivot axis 20. As E-block 12 rotates back and forth about pivot axis 20, each of the heads (not shown) at the actuator arm tips exemplified by arm tip 16 swings across the data recording tracks of a rotating magnetic disk (not shown) in the manner well-known in the art for such swing-type actuator assemblies.
An electrical coil 22 is attached to E-block 12 on the opposite side of axis 20 from head position 16. Coil 22 operates in cooperation with several fixed magnetic fields (not shown) and current-generating means (not shown) for forcing electrical current through coil 22 to generate a lateral force on actuator assembly 10, causing assembly 10 to rotate one way or the other about pivot axis 20 in response to the direction and magnitude of current flowing in coil 22, as is well-known in the art. A latch tang 24 may be fixed to coil 22 for interacting with a latch mechanism (not shown) for restraining actuator assembly 10 when the disk drive mechanism is inactivated. Latch tang 24, precision-wound coil 22 and E-block 12 are typically over-molded in plastic (not shown) to provide the necessary connecting structure. This construction is mass-producible and reliable but, because of the uniform metallic composition of E-block 12, actuator assembly 10 has an inherently high inertial resistance to the rotational motion required during head positioning. This high inertia reduces data access speed and may also reduce data transfer rates in some circumstances. Moreover, the machining process required to form E-block 12 is a relatively expensive manufacturing process. Reducing the mass of E-block 12 by substituting magnesium or some other lower-density metal may actually increase fabrication cost disproportionately to the improved rotational inertia because of additional fabrication steps. Also, a pivot assembly (not shown) must be somehow inserted and fixed to bore hole 18 with stability sufficient to minimize pivot-axis runout, which causes unpredictable tracking errors. Pivot bearing fastening methods known in the art include threaded fasteners, snap-rings and adhesives. Threaded fasteners and snap-rings are both relatively costly and time-consuming techniques and adhesives may introduce reliability and quality problems to the manufacturing process. A typical pivot mechanism known in the art (not shown) includes a ball-bearing mount coupled to rigid (metallic) bore hole 18 by means of snap-rings or threaded fasteners.
Practitioners in the art have proposed numerous incremental improvements to the actuator assembly design typified by actuator assembly 10 in FIG. 1. For instance, in U.S. Pat. No. 5,122,703, Fumihiko Takahashi et al. teach an improvement in joining coil 22 to E-block 12 that consists of fixing the two together by a hold member made of a thermal plastic resin having an elastic modulus greater than a specified value. In U.S. Pat. No. 5,148,071, Takahashi teaches the use of a nonconductive stiffening plate disposed over coil 22, with both coil and plate integrally molded (over-molded) to E-block 12. Both Takahashi inventions teach solutions to the coil-block joint flexure problem known to cause head tracking errors.
Similarly, in U.S. Pat. No. 5,168,184, Teruo Umehara et al. disclose a swing-actuator assembly that uses a plastic molded hold member no thicker than the coil element to connect coil and block, thereby reducing rotational inertia without losing the desired rigidity of the coil-block joint. In U.S. Pat. No. 5,168,185, Umehara et al. address the related problem of disk drive contamination caused by "flash formation" during encapsulation (over-molding) of the actuator arm assembly. Umehara et al. show how to use a diluted epoxy coating over the encapsulated swing-type actuator to prevent shedding of injection-mold plastic particles (flashes). Takahashi et al. and Umehara et al. consider only the coil-block joint rigidity issues relating to coil 22 and E-block 12 in FIG. 1.
In U.S. Pat. No. 5,382,851, Robert Loubier discloses a different swing-type actuator of the type exemplified by the actuator 26 in FIG. 2. Actuator 26 reduces rotational inertia by encapsulating a coil carrier 30 and individual metallic actuator arms exemplified by the actuator arm 28 into a central plastic body 32, thereby eliminating the heavy central body 34 (FIG. 1) of the E-block known in the art. Loubier's invention introduces several new disadvantages. The coil-block joint problem known in the art is exacerbated because most of the central portion 34 of the E-block is replaced with plastic, thereby perhaps introducing more flexibility in the alignment between coil carrier 22 and actuator arm plurality 36. Also, pivot-axis runout is increased because of increased flexibility at the inner surface of the bore hole 40. Loubier does not consider solutions to this problem beyond merely drilling into plastic pivot body 32 a bore hole 40 to accept an unspecified cartridge bearing assembly. Loubier considers no means for rigidly attaching his cartridge bearing assembly (not shown) to his molded plastic body 32.
The introduction into non-conductive plastic body 32 of individual conductive actuator arms exemplified by actuator arm 28 creates a static charge problem that is not known for monolithic metallic E-block actuator assemblies. Loubier resolves this problem by using a press-fit conductive pin 42 inserted through a series of precisely-aligned holes in the actuator arm plurality 36, as shown in FIG. 3. One end of conductive pin 42 is then coupled to a ground potential in some manner. The precise alignment of the actuator arm plurality 36 needed for insertion of grounding pin 42 requires jigging or drilling steps additional to those steps required for actuator fabrication using a monolithic aluminum block. He also suggests coupling arm plurality 36 through conductive pivot journal 38 at the edges exemplified by edge 44 (FIG. 3), or by means of a conductive plastic filler (not shown) contacting actuator arm plurality 36 in body 32. Although each of these techniques resolves the static charge accumulation problem, all introduce some particular new fabrication steps, thereby increasing manufacturing cost.
Without solutions for these and other disadvantages of the molded plastic actuator assembly known in the art, practitioners are obliged to accept unwanted new fabrication costs to obtain a desired reduction in rotational inertia. Certain of these unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.